1. Field of the Invention
The present invention relates to a bearing device for a driving wheel for rotatably supporting a driving wheel of an automobile on an automobile body.
2. Description of the Related Art
Different types of bearing devices for driving wheels of automobiles have been proposed depending on use. For example, a bearing device shown in FIG. 4 has as major structural elements a hub ring 101, an inner ring 102, rolling elements 103 and 104 of double rows, an outer ring 105, and a constant velocity universal joint 106.
The hub ring 101 is formed with an outboard raceway 107 on its outer peripheral surface and provided with a wheel-mounting flange 109 for mounting a wheel. Hub bolts 110 for fixing a wheel disk are provided on a wheel-mounting flange 109 at equal intervals in a circumferential direction. The inner ring 102 is fitted onto a small-diameter stepped portion 111 formed on an outer peripheral surface of an inboard-side end portion of the hub ring 101, and an inboard raceway 108 is formed on an outer peripheral surface of the inner ring 102.
The inner ring 102 is pressed into position with an appropriate interference in order to prevent its creeping. Raceways of double rows are constituted by the outboard raceway 107 formed on the outer peripheral surface of the hub ring 101 and by the inboard raceway 108 formed on the outer peripheral surface of the inner ring 102. The inner ring 102 is pressed onto the small-diameter stepped portion 111 of the hub ring 101, and a joint outer ring 121 is inserted into the hub ring 101 from its inboard side in an axial direction. Then, the joint outer ring 121 is fastened with the hub ring 101. With this process, an end portion of the inner ring 102 is butted against a shoulder portion 128 of the joint outer ring 121, so that the inner ring 102 is prevented from loosening and preload to a bearing portion 115 is controlled.
On an inner peripheral surface of the outer ring 105, raceways 112 and 113 of double rows are formed, which oppose to the raceways 107 and 108 of the hub ring 101 and the inner ring 102, and the outer ring 105 is provided with an automobile-body-mounting flange 114 for mounting a bearing device on automobile body. The flange 114 is fixed with bolts to a knuckle extending from a suspension device of the automobile body.
The bearing portion 115 is of a double-row angular ball bearing structure in which the rolling elements 103 and 104 are provided between a group of the raceways 107 and 108 formed on outer peripheral surfaces of the hub ring 101 and the inner ring 102 and a group of raceways 112 and 113 formed on an inner peripheral surface of the outer ring 105, and the rolling elements 103 and 104 in each row are supported by cages 116 and 117 at equal intervals in a circumferential direction.
At opening portions of both ends of the bearing portion 115, a pair of seals 118 and 119 sealing an annular space formed by the outer ring 115, the hub ring 101 and the inner ring 102 is fitted into an inside of the hole at an end portion of the outer ring 105 so as to prevent leakage of grease filled inside and ingress of water or foreign matters from outside.
The constant velocity universal joint 106 comprises the joint outer ring 121 provided at one end of the shaft 139 and formed with the track groove 120 on its inner peripheral surface, a joint inner ring 141 on an outer peripheral surface of which a track groove 140 opposing to the track groove 120 of the joint outer ring 121 is formed, balls 142 installed between the track groove 120 of the joint outer ring 121 and the track groove 140 of the joint inner ring 141, and a cage 143 provided between the joint outer ring 121 and the joint inner ring 141 for supporting the balls 142.
The joint outer ring 121 has a mouth portion 122 accommodating the joint inner ring 141, the balls 142 and the cage 143, and a shaft portion 123, extending in an axial direction from the mouth portion 122 and being formed with a serrated portion 124 on its outer peripheral surface. The shaft portion 123 is inserted into a through-hole of the hub ring 101 so that they are fitted together through serrated portions 124 and 125 formed on the outer peripheral surface of the shaft portion 123 and an inner peripheral surface of the through-hole, respectively. Then, the constant velocity universal joint 106 is fixed to the hub ring 101 by tightening a nut 127 on an external thread portion 126 formed on an end of the shaft portion 123. Preload of the bearing portion 115 is controlled by axial forced applied by tightening the nut 127.
In the bearing device in FIG. 4, preload of the bearing portion 115 is controlled by tightening torque of the nut 127, while in the bearing device shown in FIG. 5 in which a swaging process is employed in assembling it, preload control by fastening torque of the nut 127 is not required.
In this bearing device, a projection end portion of the small-diameter stepped portion 111 of the hub ring 101 is swaged by plastically deforming it toward an outside-diameter side, and the hub ring 101 and the inner ring 102 are unitized together by the swaged portion, or a swaged portion 131, by which the inner ring 102 is prevented from loosening and preload of the bearing portion 115 is controlled. Therefore, when engaging a bolt 133 into a threaded hole 132 formed on the shaft portion 123 of the joint outer ring 121 after inserting the shaft portion 123 through the though-hole of the hub ring 101, the joint outer ring 121 is fixed to the hub ring 101 with tightening torque that is necessary and sufficient to prevent the joint outer ring 121 from loosening.
On the other hand, in a bearing device using balls as the rolling elements 103 and 104, because the contact angle is set to about 35xc2x0, loads acting on the inner ring 102 in a direction of forming a contact angle are also taken at the swaged portion 131 of the hub ring 101 butted against the shoulder portion 128 of the joint outer ring 121. Here, the term xe2x80x9ccontact anglexe2x80x9d means the angle measured between the lines of action of force transmitted to the rolling elements 103 and 104 by the raceways 107 and 108, and a plane (or a radial plane) perpendicular to the axis of a bearing.
Accordingly, the small-diameter stepped portion 111 of the hub ring 101 and the raceway 108 of the inner ring 102 tend to be deformed by loads acting in a direction of forming a contact angle. With increasing amount of deformation of the small-diameter stepped portion 111 of the hub ring 101, the possibility of breakage of the hub ring 101 and fretting between the hub ring 101 and the inner ring 102 increases. Further, an increased amount of deformation of the raceway 108 of the inner ring 102 tends to cause deterioration of rolling service life, rise in temperature on the raceway 108, and loss in axial force (or preload) caused by fretting between the inner ring 102 and the shoulder portion 128 of the joint outer ring 121. When the small-diameter stepped portion 111 of the hub ring 101 and the raceway 108 of the inner ring 102 become to tend to undergo deformation as described above, strain produced inside the bearing may cause deterioration of service life of the bearing device.
An object of the invention is to improve the service life of a bearing device by preventing strain from being generated inside the bearing device, in which the strain is caused by deformation of a hub ring and an inner ring by loads acting in a direction of forming a contact angle.
A bearing device for a driving wheel of the invention includes an outer member on an inner peripheral surface of which raceways of double rows are formed, an inner member on an outer peripheral surface of which raceways opposing to the raceways of the outer member and a wheel mounting flange are formed, rolling elements of double rows installed between each of the raceways of the outer member and the inner member, and a constant velocity universal joint having a joint outer ring of which a shaft portion is fitted into the inner member in a manner that torque is transmittable. The bearing device rotatably supports a wheel on an automobile body. In this construction, a pilot portion is provided between a base part of the shaft portion of the joint outer ring and an end portion of the inner member. A clearance of the pilot portion is preferably 0.4 mm or less.
By providing the pilot portion between the base part of the joint outer ring and the inner member as described above, loads acting in a direction of forming a contact angle prevents deformation of the end portion of the inner member, so that breakage of the inner member is prevented and fretting of the inner member is reduced. Thus, service life of a bearing device is improved, allowing providing a highly reliable bearing device having long service life.
The invention is applicable to a bearing device having an outer member integrally provided with raceways of double rows on its inner peripheral surface and a wheel mounting flange on its outer peripheral surface. Further, the invention is also applicable to a bearing device having an inner member comprising a hub ring on an outer peripheral surface of which a wheel mounting flange, one of the raceways, and a small-diameter stepped portion are formed, and an inner ring, which is a separate member, fitted to the small-diameter stepped portion and on an outer peripheral surface of which the other raceway is formed.
In the structure described above, the pilot portion is positioned on a line extending from the line of forming a contact angle for the rolling elements on the raceway of the inner member. When the pilot portion is provided, loads acting in a direction of forming a contact angle securely prevents deformation of the end portion of the inner member, thereby facilitating further improvement of service life of the bearing device.
In the structure described above, serrated portions formed on both the inner member and the shaft portion of the joint outer ring in such a manner that torque is transmittable are preferably fitted together with an interference. By doing so, the inner member and the shaft portion of the joint outer ring can be fitted together without play.
It is also preferable that a surface hardened layer is formed in an area extending from a base portion of the wheel-mounting flange to an end portion of the inner member. By doing so, rolling fatigue life is increased and fretting can be reduced by increased surface hardness of an area including the raceway of the inner member.
The present invention is characterized in that the inner member has a swaged portion in which an end portion of the inner member is plastically deformed toward its outside-diameter side, and the swaged portion is butted against a shoulder portion of the joint outer ring in a linear contact. By making the swaged portion of the inner member and the shoulder portion of the joint outer ring butt against each other in linear contact, noise from between the swaged portion of the inner member and the shoulder portion of the joint outer ring can be prevented from occurring.
The bearing device according to the invention is further characterized in that the inner member and the shaft portion of the joint outer ring are detachably fixed together in an axial direction by a fastening element. In other words, fastening the inner member and the shaft portion of the joint outer ring may be made with fastening torque of a magnitude that is necessary and sufficient for preventing the joint outer ring loosening from the inner member. Therefore, besides a bolt or a nut, a fastening member such as a clip and a snap ring may also be used for the fastening.
The invention is also applicable for a bearing device using tapered rollers as rolling elements and suitable for automobiles that are inherently heavy.
In the structure having an inner member comprising a hub ring on an outer peripheral surface of which a wheel mounting flange, one of the raceways, and a small-diameter stepped portion are formed, and an inner ring, which is a separate member, fitted to the small-diameter stepped portion and on an outer peripheral surface of which the other raceway is formed, another pilot portion is formed between the end portion of the inner ring butted against the shoulder portion of the joint outer ring and the base part of the shaft portion of the joint outer ring. By forming the pilot portion between the end portion of the inner ring and the base part of the shaft portion of the joint outer ring, deformation of the raceway of the inner ring is prevented by loads acting in a direction of forming a contact angle, so that service life of the bearing device can be improved.
In this case, from among the two pilot portions formed between the base part of the shaft portion of the joint outer ring and the hub ring, and between the base part of the shaft portion of the joint outer ring and the end portion of the inner ring, clearance of the latter pilot portion is preferably made smaller than that of the former pilot portion.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.